1. Field of the Invention
The present invention relates to a system for protecting, controlling, and monitoring a power system.
2. Description of the Related Art
In an electric power plant such as a substation, a protection and control system is provided that includes a protective relaying function for protecting substation devices constituting a power system and a monitor control function for monitoring the substation devices. In a substation-device protection and control system disclosed in Japanese Patent Application Laid-open No. 2007-116897, a merging unit that converts analog signals of voltage and current of the power system as well as device data of circuit breakers, line switches, etc., into serial digital data, is incorporated in a substation device or is provided near the substation device. The merging unit is connected to a protection and control unit via a process bus, so that data is transmitted between the merging unit and the protection and control unit as serial digital data. Thus, cost for electric cables needed for transmitting analog signals can be reduced, thereby reducing the cost for the protection and control system.
Japanese Patent Application Laid-open No. 2007-116897 discloses following two system configurations for the substation device protection and control system to cope with a failure in the protection and control unit. In the first system configuration, two units of hardware are provided, each having a protective function as well as a control function. Each of the units is in charge of one of the functions, and when one of the units fails, the other one performs the both functions. In the second configuration, an integrated protection and control unit that can perform the protection function as well as the control function is employed in dual units, so that when one unit fails, the other unit performs the both functions.
In other words, the conventional protection and control system essentially requires hardware comparable to a dual-unit configuration to instantly cope with a failure of the protection and control unit. Consequently, in the conventional protection and control system, cost increase is inevitable for enhancing reliability of the protection and control unit.